When an image display device is used where the influence of external light, such as ambient light, is large, there is a drawback in that an image displayed on a panel is difficult to see due to the reflection of external light. The drawback is caused because a dynamic range of the display image is narrowed due to the reflection. A contrast needs to be enhanced to effectively use an entire range of tone width in order to improve deteriorated image quality after external light is irradiated.
For example, as discussed in Japanese Laid-open Patent Publication No. 11-331598, a technique is known that equalizes a histogram in order to use an entire range of tone width from dark to bright portions.
Moreover, for example, as discussed in Japanese Laid-open Patent Publication No. 2002-140700, there is a technique to suppress an excessive contrast emphasis by generating a histogram of an image, clipping pixels equals to or greater than the certain numbers of pixels for each luminance, and uniformly allocating the total number of clipped pixels to all of the luminance.